Historical research guide · 0982 · 2014
Design of magnetized liner inertial fusion experiments using the Z facility
Adam B. Sefkow · Stephen A. Slutz · Joseph M. Koning · Michael M. Marinak · Kyle J. Peterson · Daniel B. Sinars · Roger A. Vesey
In one minute
Adam Sefkow and his colleagues at Sandia and Livermore designed, on the computer, the first fusion shots of magnetized liner inertial fusion, and then Sandia fired them. The idea is simple to picture: a metal tube about a centimetre tall, filled with deuterium gas, sitting inside a magnetic field. A pulse of nineteen million amps from the Z machine crushes the tube inward in tens of nanoseconds, a laser fires down a hole in the top to pre-warm the gas, and the magnetic field, squeezed along with the fuel, keeps the heat from leaking sideways and holds the fusion alpha particles inside to warm the plasma further. What is new here is that the calculation includes all of it at once — the laser heating, the electrodes, the fuel escaping out of the ends. The team reports what the machine should produce now, what an upgraded Z could produce, and what a seventy-million-amp successor could produce with frozen fuel.
Connection
Chapter 12 needs a worked example of the move that makes compact fusion plausible — trading brute compression for magnetisation, so that the same result is reached at a fifth of the implosion speed and a hundredth of the stagnation pressure — and this is that example, with the numbers and the machine both named. For chapter 9 it is a study of a magnetically self-insulated plasma column: the seed field is compressed by a factor of a thousand, to tens of megagauss, and that field, not density, is what confines the alphas.
From the source
The magnetized liner inertial fusion target is a solid cylindrical beryllium or aluminium liner about one centimetre tall, holding a gas fuel fill of one to five milligrams per cubic centimetre; an external coil pre-seeds an axial magnetic field of five to a hundred tesla, the accelerator’s megaampere axial current drives the implosion through the Lorentz force on a tens-of-nanoseconds timescale, and a laser delivering two to twenty-five kilojoules through an entrance hole in the top preheats the fuel to ion temperatures of fifty to five hundred electronvolts.Section I, Introduction; Figure 1, schematic of the MagLIF concept
Magnetising the fuel replaces the requirement on areal density with a requirement on the compressed field times the radius, so that fusion-relevant ion temperatures above four kilo-electronvolts are reached at convergence ratios of twenty to thirty and implosion velocities near a hundred kilometres per second — against convergence above thirty and velocities above three hundred kilometres per second in traditional inertial confinement fusion — and the stagnation pressure needed falls from hundreds of gigabars to a few.Section I, Introduction
The initial axial field is flux-compressed to five to ten kilotesla at stagnation, that is fifty to a hundred megagauss, which magnetises the fusion alpha particles so that they self-heat the plasma; magnetic Reynolds numbers run from a few thousand to ten thousand and the Hall parameter can exceed a few hundred at its peak.Section I, Introduction
Integrated HYDRA simulations predict deuterium-deuterium neutron yields of two to eight times ten to the thirteenth on Z with presently available capabilities; the first integrated experiments produced yields of half to two times ten to the twelfth at the expected three kilo-electronvolt temperature, with a convergence ratio near forty, low mix, isotropic yields and spectra, and a primary-to-secondary neutron yield ratio of forty to eighty that indicates the fuel was magnetised.Section VI, Summary and Discussion; Table II, present-on-Z column
Laser timing has an optimum, found by repeating the design simulation with the preheat trigger moved forty nanoseconds either way in five-nanosecond steps: the best moment is when the inner liner boundary begins to implode, because preheating earlier increases end losses, plasma cooling and the potential for mix, while preheating later gives less effective compression. The Z-Beamlet timing jitter of about four and a half nanoseconds keeps the shot near peak potential yield.Section IV C, Laser timing and coupling efficiency; Figure 11
Scaling the design forward, an upgraded Z at twenty-four megaamperes with six kilojoules of preheat and a forty tesla seed field simulates to a deuterium-tritium yield of three times ten to the sixteenth and a fusion energy of about eighty-five kilojoules; on a new seventy-megaampere accelerator with twenty-five kilojoules of preheat and cryogenic solid deuterium-tritium fuel, one-dimensional simulations reach ten gigajoules per centimetre with a target gain of one thousand.Section V A and V B, Design of future experiments; Table II, upgrades and new-machine columns; Figure 14
The way in
https://doi.org/10.1063/1.4890298How to cite it
Adam B. Sefkow, Stephen A. Slutz, Joseph M. Koning, Michael M. Marinak, Kyle J. Peterson, Daniel B. Sinars, Roger A. Vesey (2014) Design of magnetized liner inertial fusion experiments using the Z facility doi:10.1063/1.4890298